THE PERIODIC TABLE

DEVELOPMENT OF THE PERIODIC TABLE

Antoine Lavoisier (1743-1794) In the late 1700s Lavoisier compiled a list of all

known elements. He organized the 33 known elements into four

categories: gases, metals, nonmetals, and earths.

NEW DEVELOPMENTS

With the industrial revolution and advances in science in the 1800s, new elements were discovered.

With new discoveries meant a requirement for a new way to organize and categorize the elements.

In the 1860s chemists finally agreed on a method for determining atomic mass.

With this agreement, allowed for a new way to organize the elements.

John Newlands (1837-1898) In 1864 Newlands proposed a design for

organizing the elements. He noticed that when the elements were

arranged by increasing atomic number, their properties repeated every eighth element. He termed this pattern as the law of octaves.

This law was criticised since it did not work for ALL elements.

Meyer & Mendeleev Both Meyer and Mendeleev were also focusing

on the atomic mass of the elements. Mendeleev is credited with more of the findings

since he published before Meyer.

Mendeleev noticed that when the elements were placed in increasing atomic mass there was a periodic pattern in their properties.

Mendeleev organized the elements into columns.

His periodic table was widely accepted.

Dmitri Mendeleev was born at Tobolsk, Siberia in 1834 and died in 1907.

Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869.

Mendeleev organized the periodic table based on order of recurring chemical and physical properties.

He grouped substances with similar properties together. He left gaps where he thought undiscovered elements should be and predicted some of the properties of the undiscovered elements.

 

Moseley (1887-1915) Moseley decided to organize the elements based

on their atomic number.

There were some issues with Mendeleev’s periodic table. As more elements were discovered, they found that some of these elements did not fit into the periodic table well based on atomic mass.

Moseley’s arrangement based atomic number lead to a perfect pattern of periodic properties.

Periodic Law: the statement that there is a clear periodic pattern of chemical and physical properties of the elements when they are arranged by atomic number.

MODERN PERIODIC TABLE

The modern periodic table of elements arranges the elements into columns and rows.

The columns are known as groups or families.

The rows are known as periods.

GROUPS/FAMILIES

Group 1: Alkali Metals

They are highly reactive

Have only ONE valence electron

They are shiny, have the consistency of clay, and

are easily cut with a knife

They have low melting points

REACTIVE We will be describing elements according to

their reactivity. Elements that are reactive bond easily with

other elements to make compounds. Some elements are only found in nature

bonded with other elements. What makes an element reactive?

An incomplete valence electron level. All atoms (except hydrogen) want to have 8

electrons in their very outermost energy level (This is called the rule of octet.)

Atoms bond until this level is complete. Atoms with few valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

Group 2: Alkaline Earth Metals

They are never found uncombined in

nature

They have two valence electrons

They have higher melting and boiling points than

group 1

Transition Metals

They are good conductors of heat and electricity The compounds of transition metals are

usually brightly colored and are often used to color paints.

Transition elements have 1 or 2 valence electrons, which they lose when they form bonds with other atoms. Some transition elements can lose electrons in their next-to-outermost level

Group 13: Boron Family

This family includes a metalloid (boron), and the rest are metals.

This family includes the most abundant metal in the earth’s crust (aluminum)

Group 14: Carbon Family

Atoms of this family have 4 valence electrons.

This family includes a non-metal (carbon),

metalloids, and metals.

The element carbon is called the “basis of

life.” There is an entire branch of chemistry

devoted to carbon compounds called organic

chemistry

Group 15: Nitrogen Family

The nitrogen family is named after the element

that makes up 78% of our atmosphere.

This family includes non-metals, metalloids, and

metals.

Atoms in the nitrogen family have 5 valence

electrons. They tend to share electrons when

they bond

Group 16: Oxygen Family

Atoms of this family have 6 valence electrons.

Most elements in this family share electrons

when forming compounds

Group 17: Halogens

Halogens have 7 valence electrons, which

explains why they are the most active non-

metals. They are never found free in nature

Halogen atoms only need to gain 1 electron to fill

their outermost energy level.

They react with alkali metals to form salts

Group 18: Noble Gases

Noble Gases are colorless gases that are extremely un-

reactive.

One important property of the noble gases is their inactivity.

They are inactive because their outermost energy level is full.

Because they do not readily combine with other elements to

form compounds, the noble gases are called inert.

The family of noble gases includes helium, neon, argon,

krypton, xenon, and radon.

All the noble gases are found in small amounts in the earth's

atmosphere

Rare Earth Metals

The thirty rare earth elements are composed of

the lanthanide and actinide series.

One element of the lanthanide series and most

of the elements in the actinide series are called

trans-uranium, which means synthetic or man-

made